1. Field of the Invention
The invention relates to tissue cauterization. More particularly, the invention concerns an electrocautery system with various electrodes and a mechanism for automated or user-selected operation or compensation of the electrodes.
2. Description of the Related Art
Various physiological conditions call for tissue and organ removal. A major concern in all tissue removal procedures is hemostasis, that is, cessation of bleeding. All blood vessels supplying an organ or a tissue segment to be removed have to be sealed, either by suturing or cauterization, to inhibit bleeding when the tissue is removed. For example, when the uterus is removed in a hysterectomy, bleeding must be inhibited in the cervical neck, which must be resected along the certain vessels that supply blood to the uterus. Similarly, blood vessels within the liver must be individually sealed when a portion of the liver is resected in connection with removal of a tumor or for other purposes. Achieving hemostasis is necessary in open surgical procedures as well as minimally invasive surgical procedures. In minimally invasive surgical procedures, sealing of blood vessels can be especially time consuming and problematic because there is limited access via a cannula and other small passages.
Achieving hemostasis is particularly important in limited access procedures, where the organ or other tissue must be morcellated prior to removal. Most organs are too large to be removed intact through a cannula or other limited access passage, thus requiring that the tissue be morcellated, e.g. cut, ground, or otherwise broken into smaller pieces, prior to removal.
In addition to the foregoing examples, there exist a variety of other electrosurgical instruments to seal and divide living tissue sheets, such as arteries, veins, lymphatics, nerves, adipose, ligaments, and other soft tissue structures. A number of known systems apply radio frequency (RF) energy to necrose bodily tissue. Indeed, some of these provide significant advances and enjoy widespread use today. Nevertheless, the inventors have sought to identify and correct shortcomings of previous approaches, and to research possible improvements, even when the known approaches are adequate.
In this respect, one problem recognized by the inventors concerns the small size of today's electrode structures. In particular, many electrosurgical instrument manufacturers limit the total length and surface area of electrodes to improve the likelihood of completely covering the electrodes with tissue. This small electrodes strategy results in the surgeon having to seal and divide multiple times to seal and divide long tissue sheets adequately. Such time consuming processes are also detrimental to patients, increasing anesthetic time and potentially increasing the risk of injury to surrounding structures, as the delivery of energy and division of tissue is repeated again and again.
The consequences of partial electrode coverage can be significant. This condition can cause electrical arcing, tissue charring, and inadequate tissue sealing.
Mechanical, e.g. blade, or electrosurgical division of tissue is performed immediately following tissue sealing, and the division of inadequately sealed tissue can pose a risk to the patient because unsealed vessels may hemorrhage. Arcing presents its own set of problems. If electrocautery electrodes generate an arc between them, instead of passing RF energy through targeted tissue, the tissue fails to undergo the intended electrocautery. Furthermore, depending upon the path of the arc, this might damage non-targeted tissue. Another problem is that adjacent electrodes in a multiple electrode system may generate electrical cross-talk or generate excessive thermal effect in the transition zone between two adjacent electrodes that fire sequentially. Previous designs prevented this by imposing a mechanical standoff for the jaws that the electrodes were fastened onto. However, this standoff prevented very thin tissue from making contact with the opposing electrodes, preventing an optimal electrical seal in these regions. These standoffs, if too shallow, can also result in arcing between electrodes.
At typical radiofrequency energy (RF) frequencies in the 300 kHz to 10 MHz range, tissue impedance is largely resistive. Prior to tissue desiccation, initial impedances can vary greatly depending on the tissue type and location, vascularity, etc. Thus, to ascertain the adequacy of tissue electrode coverage based solely on local impedance is imprecise and impractical. A feasible and dependable methodology for determining electrode coverage by tissue would allow for the development of electrodes of greater length and surface area for use in the safe and rapid sealing and division of tissue sheets during surgical procedures. It would therefore be advantageous to provide a methodology for determining the area of tissue coverage of one or more electrodes.